Not really that tough of a decision. I went with the most common size they put on FJ's... 285/70-17 and then made one adjustment.
First of all do NOT try spacers as they cause all sorts of rubbing.
In the front of the tires the 285's will rub this piece of plastic. 255's probably will too.
To remedy it all you have to do is undo this one Philips head screw, pull the plastic back an inch or two, make a new hole and rescrew it in. Walla... Never had a rubbing issue again even at FULL compression.
I have a
tiny rubbing on the frame rail passenger side at full lock to the right. I barely let up on the steering wheel and it stops. I bet the 255's will do the same.